The Stridsvagn 103 (Strv 103), also known as the S-Tank, is a Swedish post-World War II main battle tank, designed and manufactured in Sweden. It was developed in the 1950s and was the first main battle tank to use a turbine engine and the only mass-produced tank since World War II to dispense with a turret. It has an unconventional design with a unique gun laying process: it is turretless with a fixed gun traversed by engaging the tracks (like the 75mm gun on the 1930s French Char B1) and elevated by adjusting the hull suspension. The result was a very low-profile design with an emphasis on survivability and heightened crew protection level. Strv 103s formed a major portion of the Swedish armoured forces from the 1960s to the 1990s, when, along with the Centurions, it was replaced by the Leopard 2 variants Stridsvagn 121 and Stridsvagn 122. While most turretless armoured fighting vehicles are classified as assault guns or tank destroyers, the Strv 103 is considered a tank since its designated combat role matched those of other tanks within contemporary Swedish doctrine.
Stridsvagn 103C - an upgrade programme was started in 1986 to fit all vehicles with improved fire control systems. Also, each Strv 103 was fitted with a dozer blade, rather than just one per platoon. A further upgrade in 1987/88 replaced the Rolls-Royce engine with a newer 290 horsepower (220 kW) Detroit Diesel with additional fuel cans placed along the sides to function as applique armour, and added a new laser rangefinder.